The present invention relates to spectral radiation or light sources and more particularly to hollow cathode spectral light sources. Such hollow cathode light sources are used to generate spectral line emission which is characteristic of the cathode material. This generated light is used in a variety of spectrophotometric chemical analysis techniques, such as atomic absorption spectroscopy, for identifying chemical samples and determining the sample material concentration.
The spectral light output from a hollow cathode light source is desirably stable after a short warm-up period to minimize testing changes during operation. For certain metallic cathode materials it is difficult to achieve stable operation without a long warm-up period which reduces the efficiency of the laboratory procedure. For highly reactive materials such as calcium this is a particular problem. Calcium is difficult to handle and machine because of its reactivity with air and moisture, and is difficult to out-gas during lamp manufacture without an extended seasoning process.
It has therefore been the practice to alloy calcium and other similarly reactive metals with a stable metal such as aluminum as taught in U.S. Pat. No. 3,183,393. It has also been the practice to include another metal such as magnesium in such calcium-aluminum alloy cathodes to provide a multi-element cathode and spectral emission capability.
When calcium has been alloyed with aluminum, and aluminum and magnesium, it has still required a long warm-up period to achieve a stable spectral output of less than 2% drift per 5 minute operation. It has also been necessary to repeatedly process and season such cathodes during the manufacturing process to achieve even this stability.
It has been known in the art to alloy silver with highly volatile cathode metals such as arsenic for the purpose of keeping the arsenic from volatilizing too rapidly from the cathode. These arsenic-silver alloy cathodes have typically employed about 40 weight percent arsenic and 60 weight percent silver.